1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device, and more particularly to an apparatus for driving an LCD device and a driving method using the same for naturally displaying various images on an RGBW type display.
2. Discussion of the Related Art
Recently, various flat-panel displays have been developed to overcome disadvantages of cathode ray tube (CRT) displays such as heavy weight and high depth. Flat-panel displays include liquid crystal displays (LCDs), field emission displays (FEDs), plasma display panels (PDPs), and light emitting displays (LEDs).
Among the flat-panel displays, the LCD device includes a TFT (thin film transistor) substrate, color filter substrate, and a liquid crystal layer. Generally, a plurality of liquid crystal cells, which are arranged in an area defined by a plurality of data lines and a plurality of gate lines, are formed on the TFT substrate. Each of liquid crystal cells define a liquid crystal pixel, and a TFT, which acts as a switching device, is formed in each liquid crystal pixel. Color filters are formed on the color filter substrate and the liquid crystal layer is formed between the TFT substrate and the color filter substrate.
The LCD device generates an electric field in each pixel according to data signals applied to the data lines and reproduces various images by controlling transmissivity of the liquid crystal layer. Because degradation occurs when an electric field is applied to the liquid crystal in a particular direction for a long period of time, the polarity of a data signal is reversed for each frame, column, or dot to prevent such damage.
The LCD device makes an image by mixing red, green, and blue lights provided by 3-color pixels of red (R), green (G), and blue (B). However, in general, light efficiency of a typical LCD device for displaying one sub-pixel using 3-color dots of red (R), green (G), and blue (B) is relatively low. More specifically, since a color filter arranged in each sub-pixel of red (R), green (G), and blue (B) allows about ⅓ of incident light to penetrate the filter, light efficiency is significantly reduced.
In order to maintain the color realization ratio and to improve the light efficiency in the LCD device, Korean Patent publication No. P2002-13830 (“LCD Device”) and Korean Patent publication No. P2004-83786 (“Apparatus for Driving of Display Device and Method for Driving Thereof”) discloses an RGBW type LCD device, which includes a white color filter W in additional to the red, green, and blue color filters. The above-described RGBW type LCD device converts a 3-color image signal into a 4-color image signal, thereby increasing brightness of a color image.
FIG. 1 illustrates a view of a color area to be embodied in an RGBW type display device according to the related art. FIG. 1 shows Gamut plane coordinates with red (R) and green (G) axes displayed in three-dimensional orthogonal coordinates with red (R), green (G) and blue (B) axes. A square area indicated by solid lines represents colors to be displayed by a 3-color image signal, and a hexahedron area indicated by thick solid lines represents colors to be displayed by a 4-color image signal. That is, the RGBW type liquid crystal display device extends a color area in a diagonal direction as indicated by dotted lines adding white (W) to a 3-color of red (R), green (G), and blue (B). As a result, in a process for converting a 3-color image signal into a 4-color image signal, each coordinate in the square is extended into coordinates in the hexahedron.
In the RGBW type LCD device, an apparatus for converting a 3-color image signal into a 4-color image signal has various gain curve characteristics G1, G2, G3, and G4. Even though the gain curves G1, G2, G3, and G4 vary, brightness amplification factors in the gain curves G1, G2, G3, and G4 with respect to white (W) are the same. However, each 3-color image signal (A) with respect red (R), green (G), and blue (B) colors has a different amplification factor, such as A′, A″, and A′″. Accordingly, the brightness amplification factors of white (W) and any 3-color image signal (A) in any one of the gain curves are different from each other.
For example, when an image in which pure color with a gain value of “1” and tone color with a gain value of “2” are mixed, the brightness amplification factors are considerably different. Thus, since the brightness amplification factors according to an inputted 3-color image signal in the RGBW type LCD device are different from each other, an image perceived from the RGBW type LCD device is different from that of an RGB type liquid crystal display device. In addition, the RGBW type LCD device requires an operation circuit to employ the gain curve, but it is difficult to design the operation circuit to perform complicated operations.